1. Field of the Invention
The present invention relates to an oscillation stabilization circuit which can control time, at which an oscillation signal is stabilized, by adjusting a bias current such that the time for stabilization of oscillation signal can be advanced. The oscillation stabilization circuit can detect accurate stabilization time and can notice the time to a CPU (Control Processing Unit), thereby enhancing operational efficiency of the CPU.
2. Description of the Related Art
In general, IC elements use an oscillation signal generated from a crystal oscillator provided outside.
However, since the crystal oscillator oscillates using noise when initially operating, it takes a long time until an oscillation signal is stabilized, and accurate stabilization time cannot be noticed to a CPU. Therefore, time required for the operation of the CPU is significantly wasted. Accordingly, there is a need for a circuit which, when an oscillation signal generated from the crystal oscillator is stabilized, can notice the information.
FIG. 1 is a block diagram of a conventional oscillation stabilization detecting circuit. As shown in FIG. 1, the conventional oscillation stabilization detecting circuit includes a crystal oscillating section 210, a voltage detecting circuit 10, an oscillation stoppage detecting section 30, and an oscillation stoppage detection control circuit 40.
The conventional oscillation stabilization detecting circuit constructed in such a manner generates such signals as shown in FIG. 4. The voltage detecting circuit 10 is configured in such a manner as shown in FIG. 2, and the oscillation stoppage detecting circuit 30 is configured in such a manner as shown in FIG. 3.
Referring to FIGS. 1 to 4, an operational process of the conventional oscillation stabilization detecting circuit will be described as follows.
First, when crystal is oscillated by the crystal oscillating section 201, an oscillation signal 301 output from the crystal oscillating section 201 is detected by the voltage detecting circuit 10. The voltage detecting circuit 10 outputs a stabilization signal 130 by using the detected signal 110, the stabilization signal 130 representing that the oscillation signal is stabilized.
More specifically, the oscillation signal 301 output from the crystal oscillating section 201 is output to a CPU. The CPU converts the oscillation signal into a digital signal. The voltage detecting circuit 10 detects the signal 110 having the shape of a signal 110 shown in FIG. 4 and then outputs the signal to a transistor 32 of the oscillation stoppage detecting circuit 30.
Further, the oscillation stoppage detecting circuit 30 receives the signal 110 detected by the voltage detecting circuit 10 and a signal 120 of the oscillation stoppage detection control circuit 40, the signal 120 having the shape of a signal 120 shown in FIG. 4. Accordingly, as the time passes, a capacitor 33 of the oscillation stoppage detecting circuit 30 is charged in the form of a signal 111 shown in FIG. 4.
At this time, when the charged voltage 111 becomes equal to or more than a critical voltage, a stabilization signal having the shape of a signal 130 shown in FIG. 4 is output to the CPU by buffers 34 and 35. Through the output stabilization signal, the CPU recognizes that the oscillation signal is stabilized and then operates.
However, the conventional stabilization detecting circuit cannot control the charging time of the capacitor such that the time at which oscillation signal is stabilized cannot be adjusted. Accordingly, it is impossible to advance the time for stabilization of oscillation signal.
Further, since the time for stabilization of oscillation signal cannot be adjusted, it is difficult to detect accurate stabilization time, and thus accurate stabilization time cannot be noticed to the CPU. Therefore, a lot of time is wasted for the operation of the CPU such that operational efficiency of the CPU is degraded.